In using a dental glass ionomer cement, a polymer acid including an acid such as polycarboxylic acid as the main component and a glass powder for glass ionomer cements are allowed to react to each other under the presence of water, and hardened. This kind of glass ionomer cement has excellent characteristics, for example very good biocompatibility, excellent aesthetic property of semi-transparent hardened body, excellent adhesion to tooth substrates such as enamel and dentine, and when the glass powder includes fluoride, it has anticariogenic effect by the fluoride. Thus, the glass ionomer cement is widely used in dentistry, for example for filling cavities of dental caries, for cementing crowns, inlays, bridges and orthotic bands, for cavity linings, sealers for filling root canals, abutment construction, preventive sealings, and so on.
In order to improve the characteristics of the dental glass ionomer cement hardened body, such as the transparency and acid resistance, glass powders for glass ionomer cements to be blended in dental glass ionomer cement compositions have been developed. For example, the applicant of the present invention developed a glass powder for a dental glass ionomer cement, having a specific composition including Na and K which have an effect of lowering the refractive index of glass, and having a refraction index nd of 1.42 to 1.47 (see Patent Literature 1 for example). The refractive index nd of the glass powder is 1.42 to 1.47, which is lower than that of conventional glass powders, and the difference from the refractive index nd (approximately 1.42) of the matrix component of a practically useful dental glass ionomer cement is small. Thus, the glass powder can provide a hardened body with a high transparency. However, the glass powder tends to lower the acid resistance of the hardened body by including Na and K. In this point, the glass powder has a room for improvement.
The applicant of the present invention also developed a fluoroaluminosilicate glass powder in which a lanthanum compound, which is dissolved in the presence of polycarboxylic acid and water, exists only on the surface layers of the powder particles, for the purpose of improving the acid resistance of dental glass ionomer cement (see Patent Literature 2 for example). However, adjustment of the hardening speed of cement is also important for the dental glass ionomer cement, and as the method for adjusting the speed, generally carried out are treatments on the surface of the fluoroaluminosilicate glass powder by acid and the like. The technique of Patent Literature 2 carries out a treatment on the surface of the fluorialuminosilicate glass powder, therefore has a problem of difficulty in satisfying both of the treatment and the method for adjusting the hardening speed of the cement.